1. Field of the Invention
The present invention relates to a bulb socket for use mainly in automotive lights and, more particularly, to a bulb socket for a bulb of the kind having two filaments each connected to positive and negative terminals provided inside the bulb socket. The present invention has been made to provide a bulb socket with improved negative and positive terminals so as to prevent the negative terminal from short-circuiting with the positive terminal even when the negative terminal moves away from the normal position in the socket.
2. Description of the Prior Art
In FIGS. 5 and 6, a conventional bulb socket for housing a single-filament bulb having one filament is shown. A negative terminal 2 and positive terminal 3 are provided by insertion to the bulb socket 1 (FIG. 5). A bulb 4, indicated by an imaginary line in FIG. 6, is inserted to the bulb insertion opening 1a of the bulb socket 1. The bulb-side contacting element 2a of the negative terminal 2 contacts the negative electrode of the outside circumference of the bulb base 4a. A bulb-side contacting element 3a of the positive terminal 3 contacts the positive electrode 4b of the bulb base 4a. A connector element 2b of the negative terminal 2 and a connector element of the positive terminal 3 project into a connector insertion part 1b of the bulb socket 1, in which each of connector elements are connected with external connectors (not shown) inserted to the connector insertion part 1b.
The positive terminal 3 is securely held in the bulb socket 1 because the bulb-side contacting element 3a is pressured from above by the bulb 4. Because the negative terminal 2 is held in the socket 1 only by an engaging piece 2c engaged with the lock channel 1c of the bulb socket 1, it is not securely locked. And because the engaging piece 2c is often extremely small and has no engaging margin, the negative terminal 2 is not securely locked in some cases.
In particular, when installed in a motor vehicle and subjected to vibrations, etc., for extended periods of time, the engaging piece 2c easily disengages. When the engaging piece 2c disengages and is removed from an insertion hole 1d, a base part 2d of the negative terminal 2 contacts the curved contacting element 3a of the positive terminal 3 positioned thereabove at an encircled area X in FIG. 6.
In FIG. 7, another conventional negative terminal proposed in Japanese Utility Model Laid-open Publication (unexamined) No. H4-136890 issued Dec. 21, 1992 is shown. In FIG. 8A, the conventional bulb socket 2 viewed at other angle than at FIG. 6 is shown. This negative terminal 2 comprises a projection 2f projecting from the flat member below the bulb-side contacting element 2a. The projection 2f projects inside of the bulb insertion opening 1a when the negative terminal 2 is installed in the bulb socket 1.
When the engaging piece 2c disengages from the lock channel 1c, the negative terminal 2 comes out from the insertion hole 1d and moves toward the bulb-side contacting element 3a located thereabove. Before the top of a base part 2d of the negative terminal 2 contacts the contacting element 3a at a position P on a dot line L, the front edge 2s of projection 2f abuts on the shoulder of bulb base 4a, so that the negative terminal 2 is stopped thereat so as not to contact with the positive terminal 3. Thus, the short-cutting of the negative terminal 2 with the positive terminal 3 is prevented.
In FIG. 8B, a relationship of the gap between the negative terminal 2 and the positive terminal is shown. In the case of a single bulb shown in FIG. 5, the base part 2d of the negative terminal 2 is positioned at the bottom side of the bulb-side contacting element 3a of the positive terminal 3, and there is a large gap G2 between the base part 2d and the contact point P of the bulb-side connector 3a directly above.
Because there is a large gap G2 with a single bulb, and said gap G2 is larger than the gap between the bottom of the bulb base 4a and the projection 2f of the negative terminal 2 in the normal engagement position, the projection 2f is always stopped by the bulb base 4a before the base part 2d of the negative terminal 2 contacts the contacting element 3a of the positive terminal 3, preventing short-circuiting.
As described above, when a single-filament bulb 4 is installed in the bulb socket 1 provided with a single of positive terminal 3 and negative terminal 2, the negative terminal 2 shaped as described above is kept from contacting with the positive terminal 3.
However, in the case of the bulb socket 1 which is used for housing a double-filament bulb 4 having two filaments, two positive terminals 3 and one negative terminal 2 are provided therein, as shown in FIGS. 9 and 10A. Specifically, the negative terminal 2 is positioned under the one of the bulb-side contacting elements 3a positioned parallel to each other on the bottom side of the bulb insertion opening 1a. In other words, since the bottom of the bulb-side contacting element 3a is positioned directly above the base part 2d, it is impossible to form a gap G1 having a greater clearance between the base part 2d and a contact point P on the bottom surface of bulb-side contacting element 3a. As a result, the gap G1 is smaller than the gap G6 formed between the bottom of bulb base 4a and the projection of the negative terminal 2f, as best shown in FIG. 10A.
In FIG. 10B, the relationship of the gaps formed among the negative terminal 2, positive terminal 3, and bulb base 4a inside thus formed bulb socket 2 is shown. Since the gap G1 is smaller than the gap G6, the base part 2d contacts with the contact point P of bulb-side contacting element 3a before the projection 2f is stopped by the shoulder of bulb base 4a, and thus the short-circuiting can not be prevented.